Early Saturday morning risers are set for a celestial feast as scientists predict the moon to glow blood red thanks to the longest lunar eclipse this century. Starting from 4am on the east coast of Australia, and from 2am in the west, as the moon moves into the Earth's shadow it will gradually become darker and glow progressively redder over the next hour and a half. East coast viewers will see the blood moon at its fullest at about 5.30am, with the Earth, moon and sun in perfect alignment. The colour of the moon is affected by the light from the sun's movements skimming through the Earth's atmosphere and continuing up to space about 350,000 kilometres away. "What we're seeing is essentially all the sunrises and sunsets on the Earth, dramatically projected onto the surface of the moon," Australian National University astronomer Brad Tucker told AAP. This marks the second total lunar eclipse this year visible from Australia, with the next one predicted for 2021. Given the moon will be at its furthest distance from Earth, Professor David Coward from the University of Western Australia is forecasting a particularly dramatic lunar eclipse for those in the east. "The red colour depends on the atmosphere at the time, but my suspicions are it will be redder than normal in Sydney because you'll be looking through a thick layer of atmosphere," Prof Coward told AAP. The best vantage point to watch the blood moon will be anywhere with an unobstructed view to the west. Unlike a solar eclipse which is only visible from a particular spot at the right time, a lunar eclipse can be seen from everywhere in Australia and without special instruments - weather permitting. Bureau of Meteorology senior forecaster Jenny Sturrock is confident most of Australia will be able to view the moon, but some parts of Western Australia, New South Wales and Victoria may be affected by cloud coverage during the prime viewing period between 5am and 6am. In NSW, the view from the northwest plains, central western slopes and central tablelands may be obscured by clouds, while the southeast coastal district of Western Australia may be affected by a cold front moving through. "It's safe to say the viewing across Australia will generally be pretty good; most of the capital cities will be able to see something," Ms Sturrock told AAP. Professor Coward is urging Australians across the nation to set their alarms to catch the viewing, or even to continue revelling into the wee hours of the morning. "Watching that interaction, watching our atmosphere play a role in this visual and very beautiful spectacle, there's also science in there, the same science which took hundreds of years to work out why the sky is blue," Prof Coward said. "This moon is related to the same thing." THE RIGHT ALIGNMENT A lunar eclipse occurs when the sun, Earth and moon are in a straight line. As the sun lights up one side of the Earth it casts a shadow into space. When the moon starts passing into that shadow it becomes darker, eventually turning redder from sunlight passing through Earth's atmosphere. WHY NOT EVERY FULL MOON? Lunar eclipses happen during a full moon, but do not occur every full moon. This is because the orbit of the moon varies, tilted about five degrees as it moves around Earth, and therefore it is not always in the Earth's shadow. DIFFERENCE BETWEEN SOLAR AND LUNAR ECLIPSE? A solar eclipse occurs when the moon passes between the Earth and the sun, casting a shadow over the Earth. A lunar eclipse takes place when the moon moves into the Earth's shadow. VISIBILITY? Protective filters are advised for people gazing at a solar eclipse, while a lunar eclipse is completely safe to view with the naked eye, and far more visible than a solar eclipse. ARE THEY RARE? On average a lunar eclipse can be seen in Australia every 2.8 years. Two lunar eclipses occurred in 2018 - January 31 and July 28. The next lunar eclipse is predicted for 2021. Australian Associated Press

Early Saturday morning risers are set for a celestial feast as scientists predict the moon to glow blood red thanks to the longest lunar eclipse this century.

Starting from 4am on the east coast of Australia, and from 2am in the west, as the moon moves into the Earth's shadow it will gradually become darker and glow progressively redder over the next hour and a half.

East coast viewers will see the blood moon at its fullest at about 5.30am, with the Earth, moon and sun in perfect alignment.

The colour of the moon is affected by the light from the sun's movements skimming through the Earth's atmosphere and continuing up to space about 350,000 kilometres away.

"What we're seeing is essentially all the sunrises and sunsets on the Earth, dramatically projected onto the surface of the moon," Australian National University astronomer Brad Tucker told AAP.

This marks the second total lunar eclipse this year visible from Australia, with the next one predicted for 2021.

Given the moon will be at its furthest distance from Earth, Professor David Coward from the University of Western Australia is forecasting a particularly dramatic lunar eclipse for those in the east.

"The red colour depends on the atmosphere at the time, but my suspicions are it will be redder than normal in Sydney because you'll be looking through a thick layer of atmosphere," Prof Coward told AAP.

The best vantage point to watch the blood moon will be anywhere with an unobstructed view to the west. Unlike a solar eclipse which is only visible from a particular spot at the right time, a lunar eclipse can be seen from everywhere in Australia and without special instruments - weather permitting.

Bureau of Meteorology senior forecaster Jenny Sturrock is confident most of Australia will be able to view the moon, but some parts of Western Australia, New South Wales and Victoria may be affected by cloud coverage during the prime viewing period between 5am and 6am.

In NSW, the view from the northwest plains, central western slopes and central tablelands may be obscured by clouds, while the southeast coastal district of Western Australia may be affected by a cold front moving through.

"It's safe to say the viewing across Australia will generally be pretty good; most of the capital cities will be able to see something," Ms Sturrock told AAP.

Professor Coward is urging Australians across the nation to set their alarms to catch the viewing, or even to continue revelling into the wee hours of the morning.

"Watching that interaction, watching our atmosphere play a role in this visual and very beautiful spectacle, there's also science in there, the same science which took hundreds of years to work out why the sky is blue," Prof Coward said.

"This moon is related to the same thing."

What makes the moon appear blood red during a lunar eclipse?

THE RIGHT ALIGNMENT

A lunar eclipse occurs when the sun, Earth and moon are in a straight line. As the sun lights up one side of the Earth it casts a shadow into space. When the moon starts passing into that shadow it becomes darker, eventually turning redder from sunlight passing through Earth's atmosphere.

WHY NOT EVERY FULL MOON?

Lunar eclipses happen during a full moon, but do not occur every full moon. This is because the orbit of the moon varies, tilted about five degrees as it moves around Earth, and therefore it is not always in the Earth's shadow.

DIFFERENCE BETWEEN SOLAR AND LUNAR ECLIPSE?

A solar eclipse occurs when the moon passes between the Earth and the sun, casting a shadow over the Earth. A lunar eclipse takes place when the moon moves into the Earth's shadow.

VISIBILITY?

Protective filters are advised for people gazing at a solar eclipse, while a lunar eclipse is completely safe to view with the naked eye, and far more visible than a solar eclipse.

ARE THEY RARE?

On average a lunar eclipse can be seen in Australia every 2.8 years. Two lunar eclipses occurred in 2018 - January 31 and July 28. The next lunar eclipse is predicted for 2021.